Method and unit for efficient reporting of scheduling information in a wireless telecommunications system

ABSTRACT

A method in a wireless communication system for reporting buffer information includes selecting a format for a buffer report based on a number of radio bearer groups, k, for which data is available for transmission by a user equipment. The buffer report indicates a respective buffer fill level for one or more radio bearer groups associated with the user equipment. The method also include encoding a buffer fill level for one or more radio bearer groups in a buffer report in accordance with the selected format and transmitting the buffer report.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International ApplicationPCT/EP2006/011187, with an international filing date of Nov. 22, 2006,which corresponds to the national-stage entry U.S. patent applicationSer. No. 12/306,071, filed Dec. 12, 2008, and which claims priorityunder 35 U.S.C. §119 to Swedish Application No. SE 0601381-7, filed Jun.21, 2006, and the contents of all of the preceding are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to methods and arrangements in atelecommunication system, in particular to an efficient buffer statusencoding.

BACKGROUND AND SUMMARY

In the study item UTRAN long term evolution (LIE) initiated by the 3rdGeneration Partnership program (3GPP) it has been decided that ascheduling mechanism similar to the one used in Enhanced D-ChannelHandler (E-DCH) shall be adopted for LTE. The scheduler in a Node Bschedules resources in both downlink and uplink. In the uplink, thescheduler needs information about the data that is available in thebuffers of the user equipments (UE). This is achieved by transmittingscheduling information messages from the user equipment to the Node B.The scheduling information is transmitted as part of the Medium AccessLayer Protocol (MAC) and can therefore be either piggybacked with othertransmissions (when those are ongoing) or be sent stand alone bycreating MAC PDUs just to transfer the scheduling information. Thescheduling information in E-DCH has the format depicted in FIG. 1. HLIDdenotes the Highest priority Logical channel ID; TEBS denotes the TotalE-DCH Buffer Status; HLBS denotes the Highest priority Logical channelBuffer Status (which is a value that is coded relative to TEBS, i.e. apercent of indicated TEBS value); and UPH denotes the UE Power Headroom(which field relates to the power used in the UE). When the schedulinginformation is received in the Node B, the scheduler can determine thelogical channel that has the highest priority (HUD), how much data thatis stored in the UE buffer for this logical channel (HLBS), and thetotal UP buffer size (TEBS). In total this information is encoded in 13bits.

In a long-term evolution (LIE-) system there is a desire to employ asfiner granularity on the QoS than is possible in E-DCH. The E-DCHsolution has some limitations. If the user equipment has data on severallogical channels (radio bearers) it is only possible to see the amountof data on the channel with the highest priority. It is, however, notpossible to know if the remaining data has rather high, low, or very lowpriority. It is neither possible to know how the data is distributed,between these priorities. This means that it is difficult to achieveservice differentiation for any other service than the one with highestpriority.

A prior-art solution to this problem is to signal the buffer status perradio bearer (or per priority/QoS class). In order to achieve areasonable low size of the buffer status message the number of bits forthe buffer size of each radio bearer (or priority/QoS class) needs to berather low, e.g. 2 bits per buffer as will be used in the following.This solution, however, implies the disadvantage that it provides a verypoor granularity when in comes to the total buffer size of the userequipment. When assuming, for example, that there is only data availablefor one radio bearer the total UE buffer is then encoded with only 2bits, which is not sufficient. Clearly the number of bits per buffer canbe increased, but that leads to a large buffer status message. Oneconceivable option could be to encode the total buffer size separately.In that way relatively few bits could be used to encode the buffer sizefor each radio bearer (e.g. 2 bits) and an additional N bits could beused to encode the total buffer size. This would result in both a roughview of the buffer size per radio bearer as well as a reasonableaccurate indication of the total buffer size. However, this would alsolead to a large total buffer status message.

Other reasons of having a finer granularity than the E-DCH schedulingsolution, include among others:

-   -   1) Starvation between QoS levels within a single UE: Low        priority data flows may be starved by higher priority traffic    -   2) Inability fir the operator to control cell capacity        partitioning between QoS classes: Scheduler can in E-DCH not        know which radio bearers that have data (except for the highest        priority radio bearer which is indicated explicitly)    -   3) Low-priority traffic hitching a free ride: Low priority data        may get a free ride when high priority data is scheduled if the        scheduler is not aware how much data that is available on        different radio bearers

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method andarrangement for achieving an efficient encoding of the schedulinginformation (buffer status information) in a wireless system such as,e.g., a LTE-system or a High Speed Packet Access (HSPA) evolutionsystem, to provide—with as few bits as possible—a sufficient indicationof the amount of available data on different radio bearers and a finegranularity on the total UE buffer size.

It is thus an advantage of the present invention that it allows for anefficient way to report buffer fill levels in a wireless system, whichresults, compared to state-of-the-art solutions, in more information tothe scheduler and allowing for service differentiation while notincreasing the overhead of the status reports.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the E-DCH scheduling information format.

FIG. 2 illustrates the problem of the prior-art solution.

FIG. 3 illustrates a buffer format indicator according to the presentinvention.

FIG. 4 illustrates the format for data on a single radio bearer.

FIG. 5 illustrates the format for data on many radio bearers.

FIG. 6 illustrates a block diagram of a method according to theinvention.

FIG. 7 block diagram of an arrangement according to the invention.

DETAILED DESCRIPTION

The present invention provides an adaptive buffer status format wherethe user equipment autonomously, or by help of appropriate criteria,selects the format that is most efficient for the momentary buffercontent. The encoding of the buffer fill levels for the case of severalradio bearers uses the information from the buffets on the individualradio bearers in order to reduce the number of bits needed to encode theinformation of the total UE buffer size.

Generally, the invention relates to a method in as wirelesscommunication systems for efficient reporting of scheduling informationprocessed in a unit of said system, as illustrated in FIG. 6. The methodcomprises the steps of: adaptively selecting (610) a buffer statusformat 615 for indicating the buffer fill levels of the scheduler; andencoding (620) the buffer fill levels. The encoding step is to reduce625 the number of bits needed to encode the information of the totalbuffer size.

A first embodiment of the present invention relates to an adaptivebuffer status report format. The format of the buffer status report thatis efficient to use depends on the momentary buffer fill levels on theindividual radio bearers as well as on how many radio bearers areconfigured, which services are ongoing, etc. The user equipment shouldtherefore be allowed to select (e.g. autonomously) the format of thebuffer status report to minimize the number of bits needed (or maximizethe information that can be extracted with a fixed number of bits). Thebasic structure of the buffer status report is depicted in FIG. 3. Thebuffer format indicator field 31 (e.g. of length 1 or 2 bits) is used toindicate the format that the rest of the buffer report filed 32 isencoded with.

Below follow a few examples of buffer report formats. In these examplesthe total number of bits has been chosen as 12 but only in order toillustrate the possible relations of the field sizes in the variousformats, in practice the different formats can, however, have differentlengths since the receiver of the buffer status report can deduce thelength of the format from the buffer format indicator.

In case data is available on only one radio bearer it is efficient toindicate the radio bearer id (RBid) in a field 41, for instance oflength 3 bits, and the buffer fill level in a field 42 of a length of,e.g., 9 bits. This is shown in FIG. 4. It is expected to be a commoncase that data, is only available on a single radio bearer. This formatprovides a very high granularity of the total buffer size in that commoncase.

In order to provide service differentiation, it is necessary to reportinformation about the amount of data for different radio bearers, orgroups of radio bearers, per QoS class, per traffic priority or asimilar criterion. In the following the expression radio bearers is usedfor reasons of simplicity. In the example depicted in FIG. 5, four radiobearers are configured. The buffer fill level B, denoted Bk, for eachconfigured radio bearer k is encoded into N bit fields 51,52,53,54. Eachof the 2^(N) possible values for Bk is mapped to a buffer fill levelinterval such that, e.g., Bk=01 means a buffer fill level between 100and 500 bytes. The mapping between Bk and the buffer fill level intervalis most likely hard coded in the specifications but can also beconfigurable by higher layer signaling.

When encoding the total UE buffer B, denoted Btot, into the field 55,the information extracted from the fields B1 . . . B4 is used to improvethe granularity of the information in the following way: A sufficientestimation of the total UE buffer fill level can be obtained bysummarizing the values B1 . . . B4 such that B_estimated=B1+B2+B3+B4.The error in this estimation Err=B−B_estimated is encoded into the fieldBtot. Since the value range of Err is much smaller than the value rangeof B the granularity of Btot can be made better with this method. It canbe seen that this format gives a rough indication about the buffer filllevel on individual radio bearers as well as a medium granularity of thetotal UE buffer fill level.

An alternative coding for the case of several radio bearers is to firstencode the total size of the UE buffer in one field. Btot, and thenencode the buffer fill levels for each individual radio hearer Bk as afraction of the value indicated in Btot. The advantage compared toletting Bk and Btot indicate an absolute buffer fill level is that thevalue range of Btot is smaller than the value range of the possiblebuffer fill level.

There are several alternatives for a user equipment to select a bufferstatus format. It is one possibility that the format can be configuredvia higher layer signaling protocol (e.g. the RRC) such that a userequipment always uses the same format. This format can then bereconfigured, e.g., depending on the number of services that areconfigured according to another possibility the user equipment canautonomously select which format to use. This selection can depend,e.g., on the buffer fill levels of the individual radio bearers. Forinstance, if data is only available on one radio bearer a certain formatis selected while otherwise, i.e. for several radio bearers, anotherformat is selected. Finally, the user equipment can alternate betweenthe formats. This could achieve both a high granularity of the totalbuffer fill level as well as information about the data on individualradio bearers.

Following example gives five configured radio bearers: RRC signaling,SIP, VoIP, Video, Best effort (BE) interact access. In this example amultimedia telephony service is configured with the service componentsSIP signaling, VoIP and Video. In addition an RRC signaling radio beareris configured and a best effort bearer used for interact access. Anexample of a mapping between QoS indicator and priority order is shownin the table below tin practice the priority order would be a list ofradio bearer IDs). The mapping between QoS indicator and priority orderwould be configured in the UE via RRC signaling.

TABLE 1 QoS indicator Priority order 1 RRC, SIP, VoIP, Video, BE 2 RRC,BE, SIP, VoIP, Video 3 RRC, VoIP, Video, SIP, BE 4 RRC, Video, VoIP, SIP

In the typical case the scheduler would use QoS indicator 1 whichindicates that radio bearers should be scheduled in the default order ofpriority. In case starving occurs for e.g. the RE internet access bearerthis would be detected by the Node B scheduler and scheduling would beperformed with QoS indicator 2 for a while, which would give a higherpriority to the BE. In a similar manner, QoS indicators 3 or 4 would beused if the radio bearers carrying VoIP or Video needs more resourcesthan their default priority allows. In the last row the BE internebearer is not even included, which implies that data from this radiobearer is not allowed to be transmitted. As can be seen the RRCsignalling always have the highest priority in the example. That is alikely implementation choice but nothing prevents RRC to be downprioritized as well.

FIG. 7 illustrates an exemplary unit 700 according to the presentinvention, far example in a UE, comprising a scheduler 710 forscheduling information processed in one or more buffers 720. The unitfurther comprises a processing arrangement 730 for adaptively selectinga buffer status format for indicating the fill levels of the schedulerbuffers and an encoder 740 for encoding the buffer fill levels such asto reduce the number of bits needed to encode the information of thetotal buffer size. The unit further comprises a transmitter 750 fortransmitting an information element including the buffer status reportto other network units. The unit is described very briefly including thefunctional units essential for carrying out the invention.

The invention claimed is:
 1. A method in a wireless communication systemfor reporting buffer information, comprising: selecting a format for abuffer report based on a number of radio bearer groups k for which datais available for transmission by a user equipment, wherein the bufferreport indicates a respective buffer fill level for one or more radiobearer groups associated with the user equipment; encoding a buffer filllevel for the one or more radio bearer groups in the buffer report inaccordance with the selected format; and transmitting the buffer report;wherein selecting the format for the buffer report comprises selectingbetween at least a first format and a second format, wherein the firstformat indicates a buffer fill level associated with a single group ofradio bearers and the second format indicates a plurality of buffer filllevels each associated with a respective group of radio bearers; whereinselecting between at least the first format and the second formatcomprises: selecting the first format if only a single group of radiobearers has data available for transmission; and selecting the secondformat if more than one group of radio bearers has data available fortransmission; wherein selecting the format for the buffer reportcomprises the user equipment autonomously selecting the format.
 2. Themethod of claim 1, wherein the first format further indicates anidentifier for an associated group of radio bearers.
 3. The method ofclaim 1, wherein encoding the buffer fill level for the one or moregroups of radio bearers comprises encoding, in N bit fields, arespective buffer fill level, B_(k), for each of the k groups of radiobearers that have data available for transmission, wherein each of the2^(N) possible values for B_(k) is mapped to a buffer fill levelinterval.
 4. The method of claim 1, wherein selecting the format for thebuffer report comprises selecting the format in accordance with higherlayer signaling.
 5. An apparatus for communication in a wirelesscommunication system, comprising: a processing element configured toselect a format for a buffer report based on a number of radio bearergroups k for which data is available for transmission by a userequipment, wherein the buffer report indicates a respective buffer filllevel for one or more radio bearer groups associated with the userequipment; an encoder configured to encode a buffer fill level for theone or more radio bearer groups in the buffer report in accordance withthe selected format; and a transmitter configured to wirelessly transmitthe buffer report; wherein the processing element is configured toselect the format for the buffer report by selecting between at least afirst format and a second format, wherein the first format indicates abuffer fill level associated with a single group of radio bearers andthe second format indicates a plurality of buffer fill levels eachassociated with a respective group of radio bearers; wherein theprocessing element is configured to select between at least the firstformat and the second format by: selecting the first format if only asingle group of radio bearers has data available for transmission; andselecting the second format if more than one group of radio bearers hasdata available for transmission; wherein the processing element isconfigured to select the format for the buffer report by autonomouslyselecting the format.
 6. The apparatus of claim 5, wherein the firstformat further indicates an identifier for an associated group of radiobearers.
 7. The apparatus of claim 5, wherein the encoder is configuredto encode the buffer fill level for the one or more groups of radiobearers by encoding, in N bit fields, a respective buffer fill level,B_(k), for each of the k groups of radio bearers that have dataavailable for transmission, wherein each of the 2^(N) possible valuesfor B_(k) is mapped to a buffer fill level interval.
 8. The apparatus ofclaim 5, wherein the processing element is configured to select theformat for the buffer report by selecting the format in accordance withhigher layer signaling.